The present invention generally relates to a lighting system for illumination of an observation space, especially an observation space in which a pressurized and/or hot medium is contained.
A lighting system of this type is generally known. Lighting systems of the before-mentioned kind are used for illuminating an observation space, such as a reaction chamber or a combustion chamber in which chemical reactions, combustion processes or other physical or chemical processes take place, in order to display the development of the process outside the observation space, for example on a display unit.
A lighting system of this kind finds special application in the illumination of the combustion chamber of a combustion engine of a motor vehicle. In engine development and also in engine testing such lighting systems are used in combination with an observation system, for example a technical endoscope, for displaying the fuel injection process and the distribution of the mixture with the engine in running condition. As the observation system, i.e. the endoscope, normally works without a separate light supply, it is a requirement that the combustion chamber be illuminated with the aid of the lighting system in order to have the possibility to observe the mixture-forming processes taking place in the cylinder of the engine, which as such are not self-lighting.
To this end, an opening, i.e. a bore, is provided in the wall of the cylinder head, through which the front, i.e. the distal end of a lighting head of the lighting system is guided, whereafter the opening through which the lighting head has been introduced into the combustion chamber is sealed in a suitable way to prevent the escape of combustion gases. For observing the combustion chamber, being illuminated by the lighting system, the endoscope is introduced through a corresponding second bore provided in the cylinder head.
The lighting head is connected, via an optical-fiber cable, to a light source, for example a stroboscopic light source. The light generated by the light source is transmitted through an optical-fiber cable to the lighting head, where it emerges from the lighting head at the distal end, which latter has been introduced into the combustion chamber. For transmission of the light from the light source to the free end of the lighting head, the optical-fiber cable comprises optical fibers or optical fiber bundles.
In conventional lighting systems such optical fiber bundle is run to the distal end of the lighting head. At the distal end, the individual optical fibers are cemented together by an adhesive.
However, such a lighting system is connected with certain disadvantages. The optical fibers at the distal end of the lighting head must not get into contact with the combustion gases in the combustion chamber of the engine because the optical fibers as such, and their sealing compound as well, are resistant neither to pressure nor to high temperatures. But in the combustion chamber of an engine extremely high pressures of more than 100 bar and high temperatures, that may well exceed 200xc2x0 Celsius, prevail in the running condition of the engine. In order to protect the optical fibers from the high temperatures and the high pressures, conventional lighting systems must, therefore, be used in combination with a cup-shaped protective glass that is inserted into the opening in the wall of the combustion chamber and into which the lighting head is introduced. The use of a protective glass necessitates a bore in the cylinder head of 14 mm diameter, for the installation of the protective glass. While an opening of such a diameter was no problem with older engines, applying a bore of such a diameter in the cylinder head is no longer possible with new multi-valve engines, due to space restraints that result from the particular structural conditions. Making the total arrangement, comprising the protective glass and the lighting head, smaller would of course be possible, but would considerably reduce the light-transmission capacity and make the illumination of the observation space less effective.
In addition to the use of a protective glass it is further necessary, with conventional lighting systems, to cool the distal end of the lighting head since the protective glass, while preventing direct contact between the optical fibers and the combustion gases, does not prevent the transmission of heat radiation. The heat radiation passing the protective glass subjects the distal end of the optical fibers to high temperatures, which cause damage to the fibers and in particular to their sealing compound. Conventional lighting systems therefore require an additional cooling circuit with supply and discharge systems in the lighting head, which occupy a large part of the cross-section of the lighting head so that only a small cross-section of approximately 3.5 mm diameter remains for the optical fibers while the effective outer diameter of the lighting head is approximately 7.5 mm so that the theoretical light-transmission capacity of the lighting head is poorly utilized. And there is further the risk that in case the cooling system should fail, the optical fibers at the distal end of the lighting head and, thus, the entire lighting system may be destroyed.
Now, it is the object of the present invention to improve a lighting system of the before-mentioned type so that the disadvantages described above are avoided and the lighting system can be used without a protective glass and without a cooling system, without the risk that extreme pressure or temperature influences may cause damage to the lighting head.
With respect to the lighting system described at the outset, the invention achieves this object by providing a lighting system, comprising
an optical-fiber cable having a first end which can be connected to a light source, and a second end;
a lighting head, which is connected to said second end of said optical-fiber cable and which can be introduced into said observation space,
wherein said lighting head comprises a light guide rod made from a material which is resistant to pressure and temperature.
In the lighting system according to the invention, the optical-fiber bundle of the optical-fiber cable, instead of being guided up to the distal end of the lighting head, is therefore replaced at the lighting head by a light guide rod made from a pressure and/or temperature-resistant material. The sensitive optical fibers are, thus, located outside the observation space and are no longer exposed to the damaging influences of pressure and temperature. The light guide rod provides the advantage that there are no glued joins or cemented areas at its distal end, which project into the observation space and which might deteriorate under the effect of pressure or high temperatures. By equipping the lighting head with a light guide rod made from a pressure and/or highly temperature-resistant material, the need for a protective glass and also for cooling of the lighting head is eliminated. The light guide rod may consist of a suitable transparent glass that may come in contact with the combustion gases in the combustion chamber of a combustion engine without being damaged thereby. Due to the fact that no protective glass is required any more as protection for the lighting head, the diameter of the opening in the wall of the observation space may be reduced, for example, to 10 mm so that the lighting system according to the invention can be used also with modern multi-valve engines where a bore of larger diameter cannot be applied. In order to permit the diameter of the opening to be reduced, no scaling-down of the lighting head, which would reduce its light-transmission capacity, is required with the lighting system according to the invention. While in conventional lighting systems, due to the cooling requirement, cooling channels are provided on the lighting head which heavily reduce the cross-section of the lighting head that can be used for light transmission, another advantage of the lighting system according to the invention lies in the fact that the entire cross-section of the light guide rod is available for light transmission so that the light-transmission capacity of the lighting system according to the invention is substantially increased compared with conventional lighting systems. The light guide rod may, therefore, have the same diameter as the optical fiber bundle in the optical-fiber cable. While with conventional lighting systems only a diameter of approximately 3.5 mm is available in the lighting head for the optical fibers, the light guide rod of the lighting system according to the invention may be given a diameter of more than 6 mm which quadruplicates the light efficiency, compared with conventional lighting systems. Suited as material for the light guide rod are, in principle, all heat-resistant glasses with high transparency.
According to a preferred embodiment, the light guide rod is detachably connected to the optical-fiber cable.
This feature provides the advantage to make the light guide rod exchangeable. While in conventional lighting systems the entire lighting system is rendered unserviceable when the optical fibers, that are guided up to the distal end of the lighting head, get damaged, the invention now teaches to connect the lighting head detachably to the optical-fiber cable. In case of damage, caused for example by impact, the low-cost light guide rod can be replaced, while the expensive and temperature-sensitive optical-fiber cable can be connected to a new lighting head and can be used again. This reduces the costs of repair of the lighting system according to the invention. Another advantage of the detachable connection between the light guide rod and the optical-fiber cable is seen in the fact that it is now possible to provide a set of exchangeable light guide rods, intended for example for different illumination directions. The lighting system according to the invention, therefore, offers an advantageous modular structure. In contrast, it was a requirement with conventional lighting systems to have available a separate complete lighting system for each lighting direction, which led to correspondingly high costs.
According to a further preferred embodiment, the light guide rod is provided at its proximal end with a coupling sleeve for connecting the light guide rod with the optical-fiber cable.
This feature offers the advantage that the coupling sleeve allows an easy-to-handle, detachable connection to be realized between the light guide rod and the optical-fiber cable. If more than one light guide rods are provided for the lighting system according to the invention, for different illumination directions, each light guide rod is provided at its proximal end with a corresponding coupling sleeve so that rapid exchange of the different light guide rods is rendered possible.
It is preferred in this connection if the coupling sleeve is fixed to the light guide rod by means of an adhesive, with the refractive index of the adhesive being smaller than the refractive index of the light guide rod.
As the coupling sleeve, preferably, is made from a metal, fixing the coupling sleeve on the light guide rod can be effected most safely by gluing. Given the fact that the join between the coupling sleeve and the proximal end of the light guide rod is outside the observation space in operation, the join is not exposed to the extreme temperatures that might prevail in the observation space, but only to lower temperatures so that there does not exist any risk that a join may get detached under the effect of heat. Losses during light transmission through the light guide rod are avoided in the area of the coupling sleeve by the fact that the adhesive has a refractive index smaller than the refractive index of the light guide rod. Due to the use of an adhesive having a refractive index smaller than the refractive index of the light guide rod, the total refraction, by the surface of the light guide rod, of the light guided through the light guide rod, which is required for the light transmission through the light guide rod, is maintained. Consequently, the system advantageously provides on the one hand safe fastening of the coupling sleeve on the light guide rod, without any light losses occurring at the join between the coupling sleeve and the light guide rod. However, it may also be envisaged to solder the coupling sleeve to the light guide rod by means of a metal/glass soldering process.
According to a further preferred embodiment, the adhesive is resistant to high temperatures.
This feature offers the advantage that in the event heat should be transmitted to the adhesive through metal parts of the lighting head, the adhesive will not lose its adhesive properties under the effect of such heat so that, consequently, the join between the light guide rod and the coupling sleeve will not get detached.
According to a further preferred embodiment, the adhesive is transparent at least in the area near the surface of the light guide rod.
By making the adhesive transparent at least in the area near the surface of the light guide rod, it is prevented that part of the light may get absorbed by the adhesive at the transition between the surface of the light guide rod and the adhesive. Consequently, the entire light intensity guided through the light guide rod will be transmitted by total reflection up to the distal end of the light guide rod.
According to a further preferred embodiment, the adhesive is formulated on a silicone basis.
The use of a silicone-based adhesive provides the advantage that silicone on the one hand has a lower refractive index than glass and, on the other hand, is resistant to high temperatures. Another advantage lies in the fact that a transparent adhesive can be made on the basis of silicone. Another advantage of a silicone-based adhesive derives from the fact that silicone can be produced at low cost.
According to a further preferred embodiment, the coupling sleeve encloses the light guide rod up to approximately its distal end.
This feature provides the advantage that the coupling sleeve protects the light guide rod from impacts. This avoids the formation of notches in the surface of the light guide rod, which could impair its light-transmission capacity due to impairment of the total reflection caused by surface irregularities.
According to a further preferred embodiment, a supporting surface, supporting the proximal end face of the light guide rod in axial direction, is formed in the coupling sleeve.
This feature provides the advantage that the light guide rod is prevented from getting displaced axially in proximal direction under the effect of the high pressure prevailing in the observation space, whereby the light guide rod is prevented from being pressed against the distal end of the optical fibers and from damaging the latter.
According to a further preferred embodiment, the light guide rod is metallized on at least part of its surface.
This feature provides the advantage that the distribution of the light emerging from the distal end of the light guide rod can be optimized by the metallization on the surface of the light guide rod, especially when the metallization is provided on the distal end of the light guide rod. The metallization acts as a mirror that allows coupling-out of the light from the distal end of the optical fiber bundle in a desired direction.
It is preferred in this connection if the metallization is formed from a metal that is resistant to high temperatures and/or if the metallization is covered by a protective coating.
This feature provides the advantage that the metallization cannot be damaged by the effect of the high temperatures that may prevail in the observation space.
According to a further preferred embodiment, the light guide rod is provided with a plane or curved ground surface at its distal end.
This feature provides the advantage that the light distribution of the light emerging from the distal end of the light guide rod can be influenced in a desired way without any metallizations being required for this purpose that may under certain circumstances not withstand the high temperatures prevailing in the observation space.
It is preferred in this connection if the ground surface is plane and forms with the side line of the light guide rod a vertex angle in the range of between 20xc2x0 and 90xc2x0.
This feature provides the advantage that an oblique plane ground surface permits an almost punctiform light exit to be achieved at the vertex of the ground surface. This provides the additional advantage that the depth of penetration of the distal end of the light guide rod into the observation space, required for illuminating the operating space, can be minimized, and this in turn makes it possible, in an advantageous way, to minimize disturbing influences on the processes taking place in the observation space and the thermal load acting on the point of the light guide rod as well.
According to a further preferred embodiment, the light guide rod is made from a heat-insulating material.
This feature provides the advantage that no or only little heat is transmitted from the observation space in proximal direction, so that temperature-sensitive parts of the lighting system arranged outside the combustion chamber, such as the distal ends of the optical fibers, are not impaired by the effect of heat.
According to a further preferred embodiment, the light guide rod is made from quartz glass.
Quartz glass on the one had provides the advantage of being highly transparent so that the light can be guided into the observation space with high transmission capacity. Another advantage of quartz glass lies in the fact that it is heat-insulating. In addition, quartz glass has a small coefficient of temperature expansion, so that the high temperature gradient between the distal end of the light guide rod, which is introduced into the observation space, and its proximal end arranged outside the observation space does not result in any critical stresses in the light guide rod. In addition, quartz glass has the advantage that it is transparent across the entire optical spectrum, from infrared to ultraviolet, which makes the lighting system according to the invention also suited for spectro-scopic applications.
According to a further preferred embodiment, a rigid spacer in the form of a shaft is arranged between the lighting head and the optical-fiber cable, the light guide rod being detachably connected with the spacer.
This feature provides the advantage that the lighting head can be easily introduced into the opening in the wall of the observation space. Preferably, the dimensions of the spacer are such that the spacer rises above any components located outside the observation space, for example supply and discharge lines of a combustion engine. By fixing the light guide rod detachably on the spacer, the light guide rod can be pre-assembled with the spacer and, thus, connected to the optical-fiber cable, prior to being introduced into the opening of the observation space.
It is preferred in this connection if an insert is provided that can be fixed in the opening in the wall of the observation space outside the latter, in which case the spacer can be slid into the insert and can be fixed at the proximal end of the latter by means of a mounting element.
This feature, together with the preceding feature, further improves the operating ease of the lighting system according to the invention. The insert can at first be fitted in the opening in the wall of the observation space and can be fixed in the opening, for example, by a threaded connection. Thereafter, the spacer, which is connected to the optical-fiber cable and on which the light guide rod had been mounted before, for example by means of the before-mentioned coupling sleeve, is slid into the insert and fixed at its proximal end by means of the mounting element. The step of fixing the spacer by means of the mounting element can be carried without being hindered by any components located outside the observation space, as the spacer ensures that a suitable spacing remains to the wall of the observation space.
It is preferred in this connection if the mounting element is captively held on the spacer.
This feature has the effect to further improve the operating ease during assembly of the modular lighting system.
According to a further preferred embodiment, the mounting element is a cap nut or a bayonet ring.
A cap nut or a bayonet ring constitute, advantageously, structurally simple and easy-to-operate mounting elements.
According to a further preferred embodiment, the coupling sleeve and the distal end of the spacer can be connected by screwing.
This feature provides the advantage that the light guide rod can be connected quickly and easily with the spacer and, thus, the optical-fiber cable through the coupling sleeve.
According to a further preferred embodiment, the lighting system is designed for spectroscopically coupling-out light from the observation space.
This feature provides the advantage that the lighting system according to the invention not only permits light to be directed into the observation space, but also allows light to be coupled out from the observation space for being then subjected to spectral analysis. This is useful, especially, when studying combustion processes, for example for the spectroscopic examination of flames in combustion chambers.
In a preferred application, the lighting system according to the invention is used for illuminating a combustion chamber of a combustion engine and/or for spectroscopically coupling-out light from the combustion chamber.
According to a further preferred embodiment, the lighting system according to the invention is used for illuminating a reaction chamber in chemical industry and/or for coupling out light from such a chamber.
In a further preferred application, the lighting system according to the invention is used for illuminating a reactor of a nuclear power station.
Further advantages are evident from the description and from the appended drawings.
It is understood that the features recited above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without leaving the scope of the present invention.
An exemplary embodiment of the invention is shown in the drawings and will be explained in more detail in the description below.